Composition Of Metal Particles Research Articles

Electrical relaxations in polymeric particulate composites of epoxy resin and metal particles

Abstract Composites of epoxy resins and nickel particles in various amounts were prepared and their dielectric spectra were measured in the frequency range 5 Hz–13 MHz and temperature interval from ambient to 140°C. The formalism of electric modulus proved to be efficient in analysing and interpreting obtained data. For these composites two relaxation processes are revealed in the frequency range and temperature interval of the measurements. One is an interfacial dielectric relaxation (Maxwell–Wagner–Sillars), MWS and the other is a conductivity relaxation. They both follow the Cole–Davidson approach with the exponent γ reflecting a distribution of relaxation times with the characteristics of each process. AC conductivity of these composites is frequency and temperature dependant, it generally follows the exponential law σ ac ∼ ω s and reveals a conductivity relaxation process, in the low frequencies.

Quantum confinement effect in nanocomposites

Composites of nanometer-sized metal particles within a dielectric medium have attracted a lot of attention in recent years because of interesting properties exhibited by them. Quantum confinement effect tend to dominate the properties of carriers within the particles having nanoscale dimensions. Nanocomposites have been prepared by simple chemical methods. Optical absorption data when analyzed with Mie’s scattering formula give results which indicate a metal–insulator type transition in the case of silver particles having diameters around 3 nm. Heterostructure quantum dots involving Ag 2O nanoparticles with a thin shell of metallic silver show unusual optical absorption spectra again arising due to a confinement effect. Composites consisting of the ferroelectric phase BaTiO 3 and nanosized nickel or silver, in a gel medium show a large increase in the value of dielectric permittivity. This is explained as resulting from a quantum size effect.

DC and AC Conductivity in Polymeric Particulate Composites of Epoxy Resin and Metal Particles

The DC and AC conductivity of composites with epoxy resin and nickel particles was investigated for various content of nickel powder from ambient to 120 °C. AC conductivity was measured in the frequency range 10 Hz to 13 MHz. An enhancement of conductivity was evidenced increasing conductive filler content and temperature. AC conductivity was found to be frequency dependent beyond a critical frequency ω c. The activation energy of the temperature shift of ω c was compared to the activation energy of DC conductivity.

Characterization of highly dispersed bimetallic NiCu alloy particles by ferromagnetic resonance

Nanocomposites of the nominal composition Ni 0.4 Cu 0.6· nSiO 2 ( n=3,6,9,12,15,20) were investigated by means of ferromagnetic resonance (FMR), to study the influence of metal particle composition and size, and of the metal-matrix interaction on the FMR powder spectra. The thermomagnetic investigations ( I rel exp- T dependence) revealed that all nanocomposites except n = 20 posses a bimodal metal particle composition. The Ni-rich component with diameter 8 13 nm consists of about Ni 0.9Cu 0.1 and the Cu-rich component with diameter 5–11 nm of about Ni 0.7Cu 0.3 alloy particles. In Ni 0.4Cu 0.6·20SiO 2 only the Ni-rich component was detected. By spectral simulation the metal-matrix interaction was characterized at 273 and 423 K by compressive and tensile stress, respectively. The change in sign of the strain at 300 K below the reduction temperature points to the high mobility of the alloy.

Erosion-corrosion of carbon steel by products of coal combustion

Erosion of carbon steel by fly ash and unburned char particles was measured in the convection section of an industrial boiler firing micronized coal. The rate of erosion was enhanced by directing a small jet of nitrogen, 3 vol.% oxygen in nitrogen, or air toward the surface of a test coupon mounted on an air-cooled tube. Ash and char particles suspended in the flue gas entrained by the jet were accelerated toward the surface of the specimen. Samples were exposed for 2 h with metal temperature at 450, 550, and 650 K (350, 530, and 710°F). Changes in the surface were measured using a surface profiler. Erosion was slowest at the lowest metal temperature, regardless of the jet gas composition. Under the nitrogen jet, erosion increased with increasing temperature over the range of temperatures investigated. In the presence of 3% oxygen, erosion was most rapid at the intermediate temperature. At the highest oxygen concentration, in the air jet, the erosion rate was low at all three temperatures. The temperature and oxygen dependences of the erosion rate were consistent with a model for simultaneous erosion and oxidation. Extrapolation of the results to lower velocity, using experimentally determined coefficients for metal and oxide erosion, provided estimates of erosion of a tube, as a function of impaction angle and gas velocity. Under the conditions of metal temperature, oxygen concentration, particle size, particle loading, and particle composition investigated, erosion of carbon steel tubes is expected to be slower than 0.05 μm h −1 when the gas velocity in the convection section of the boiler is less than approximately 10 m s −1.

X-ray emission spectrometry of phase separation in Pt [sbnd]Rh nanoparticles for nitric oxide reduction

Composition determinations of individual sub-10 nm metal particles in Pt Rh/alumina by analytical electron microscopy are consistent with a low-temperature miscibility gap below about 750°C in this system. Pt-rich alloy particles are more active than pure Pt for the reduction of nitric oxide with hydrogen at temperatures ≤ 300°C. Rh-rich particles appear to have low activity for this reaction. Catalysts which contain a bimodal distribution of Pt-rich and Rh-rich particles are not as active as pure Pt. Composition versus size plots of small metal particles appear to comprise a new characterization method for supported metal catalysts.

The structure and composition of metal particles in two type 6 ordinary chondrites

Abstract— The purpose of this study is to examine, using light optical and electron optical techniques, the microstructure and composition of metal particles in ordinary chondritic meteorites. This examination will lead to the understanding of the low temperature thermal history of metal particles in their host chondrites. Two type 6 falls were chosen for study: Kernouvé (H6) and Saint Severin (LL6).In both meteorites, the taenite particles consisted of a narrow rim of high Ni taenite and a central region of cloudy zone similar to the phases observed in iron meteorites. The cloudy zone microstructure was coarser in Saint Severin than in Kernouvé due to the higher bulk Ni content of the taenite and the slower cooling rate, 3 K Ma−1 vs. 17 K Ma−1. Three microstructural zones were observed within the high Ni taenite region in both meteorites. The origin of the multiple zones is unknown but is most likely due to the high Ni taenite cooling into the two phase γ″ (FeNi) + γ′ (FeNi3) region of the low temperature Fe‐Ni phase diagram. Another explanation may be the presence of uniform size antiphase boundaries within the high Ni taenite. Finally, abnormally wide high Ni taenite regions are observed bordering troilite. The wide zones are probably caused by the diffusion of Ni from troilite into the high Ni taenite borders at low cooling temperatures.

Quantitative Pt and Rh distributions in pollution-control catalysts

In the control of automobile emissions Pt is utilized to facilitate the oxidation of CO and hydrocarbons while Rh is added to selectively catalyze the reduction of NO x to N 2. These separate functions suggest that an optimum catalyst might have these elements at different locations within the support. Two levels of noble-metal distribution are important: (a) the distribution across the 1.2 mm wall of the γ-alumina support monolith and (b) the distribution within individual 1–20 nm particles of reduced catalyst. An electron probe microanalyzer (EPMA) was used for quantitative analysis of the Pt and Rh distributions across the support wall. The EPMA can detect a minimum of 200–500 ppm of these metals in alumina, but at a spatial resolution of 10 μm. An analytical electron microscope (AEM) with a field emission electron source was used to measure the composition of small metal particles down to 1–2 nm in diameter. The high spatial resolution of the AEM analysis allowed detection of surface segregation in 1–20 nm particles containing both Pt and Ph. Platinum segregated to the particle surface as expected for Pt—Rh particles reduced in H 2.

An inductive method for estimating the composition and size of metal particles

A method for estimating the composition and size of metal particles is described. An inductive coil sensor is used which, on the introduction of a metal particle, changes impedance. The nature of the impedance change, for a given coil, depends on the composition and size of the particle which can be detected by incorporating the coil into a marginal oscillator circuit and effecting amplitude and frequency demodulation. Experimental results are given for various materials and an application of the method to lubricant wear-debris condition monitoring is described.

Composition, structure, and age of the Apollo 16 subregolith basement as deduced from the chemistry of post‐imbrium melt bombs

Irregularly shaped, slag‐like impact‐melt bombs with variolitic crystallization texture, mostly 1 to 10 cm in size, occur throughout the regolith of the Apollo 16 landing site. We have analyzed 16 samples from Stations 11 and 13 near North Ray Crater using the microscope, electron microscope, microprobe, neutron activation, and 40Ar‐39Ar age‐dating techniques. We interpret the melt rocks as rapidly quenched, high‐velocity ejecta (“glass bombs”) from impact craters less than 1.5 km in diameter located in the vicinity of the Apollo 16 landing site. A comparison between glass bombs and typical regolith samples from various sampling stations reveals differences in their bulk chemical compositions. More than 80% of the glass bombs cannot be derived from the melting of the regolith, but can be produced by melting the subregolith basement. The differences in chemical composition of metal particles in glass bombs and regolith samples are consistent with these findings. Mixing calculations show that the glass bombs were formed by melting of two or more of the most abundant lithologies (granulites, feldspathic melt breccias, anorthosites, and various mafic melt breccias of VHA and LKFM affinity) that constitute the subregolith basement. From these results, we conclude that the subregolith basement represents a polymict megabreccia target. The glass bombs are post‐Cayley in age. They were produced by several different impact events more than 370 Ma ago by which they were emplaced in proximity to the North Ray Crater area. They were buried under a younger regolith layer until the North Ray impact event 50 Ma ago brought them up to the lunar surface again, and since then they have been exposed to cosmic radiation.

Tandem deposition of small metal particle composites

A new method for preparing small metal particle composites (cermets) is described. It consists of many sequential depositions on a substrate of small amounts of a metal and an insulator from separate deposition sources. Under certain conditions, this method provides composites which, for metal volume fractions of less than about 0.5, consist of metal spheres with a very narrow size distribution embedded uniformly in the insulating matrix. In addition to the improved morphology of the composites, the new method also allows, for the first time, for control of metal particle size independent of metal volume fraction.

Dielectric response of small metal particle composites

The authors report the first measurements of the dielectric function for well characterised metal-insulator composite materials. These composite materials were prepared by a novel sputtering method and consist of uniformly sized (nanometre diameter) metal spheres embedded in the insulator matrix. The dielectric functions were measured by electron energy loss spectroscopy (EELS) and optical methods over the energy range 0.4 to 40 eV. No existing theory satisfactorily explains the results.

Absorption of far-infrared radiation by random metal particle composites

Measurements have been made of the absorption of far-infrared radiation by Pd small particles randomly embedded in KCl. The small particle specimens had Pd volume fractions between 0.001 and 0.1. At volume fractions of 0.03 and below, the absorption coefficient was proportional to the Pd concentration. The frequency dependence of the absorption coefficient was typically quadratic below 30 ${\mathrm{cm}}^{\ensuremath{-}1}$ with a slower dependence above 30 ${\mathrm{cm}}^{\ensuremath{-}1}$. The absorption coefficients were about a factor of 10 larger than those calculated from a theory based on electric and magnetic dipole absorption.

Effects of Some Factors on the Critical Preheating Temperature of Particles in Producing Metal-Particle Composites by Pressure Casting

Effects of Some Factors on the Critical Preheating Temperature of Particles in Producing Metal-Particle Composites by Pressure Casting

The chemical composition of metallic spheroids and metallic particles within impactite from Barringer Meteorite Crater, Arizona

Atomic absorption analyses of 25 metallic spheroids from Barringer Meteorite Crater have been carried out for Fe, Ni, Co and Cu. In addition, electron microprobe analyses of 58 impactite metallic particles have been carried out for Fe, Ni and Co from four different impactite samples. The normalized Ni, Co and Cu contents of the spheroids were from 13–22 per cent, 0.8–1.3 per cent and 260–430 μg/g, respectively. These figures represent enrichment factors of 2–3 in the spheroids compared to analyses of the bulk meteorite. The Co/Ni and Cu/Ni ratios in the spheroids are close to the respective ratios in the bulk meteorite. This suggests that the spheroids were formed by preferential removal of iron by oxidation from a chemically homogeneous liquid. The impactite metallic particles had Ni contents from 10 to 95 per cent and Co contents from 0·3 to 4 per cent. The Co contents of these particles showed a positive correlation with Ni up to 60 per cent Ni and a negative correlation beyond 60 per cent Ni. Reaction of the impactite metallic particles with SiO 2 of the target can explain these variations. Our findings show that extensive chemical reaction between projectile and target occurs at impact.